Categories are miscellaneous groupings of items so that they can be referenced collectively in a game rule. For example, grouping all the haulers together (creatures that can be used to pull heavy loads, such as carts and catapults), since this information cannot be derived from any other creature attribute. Then a game rule can define the creation of a war machine by referencing haulers - any creature that is able to pull heavy loads will do. In this way, items within a category become interchangeable, which makes faction design more flexible and versatile.